1. Field of Invention
The present invention relates to a vehicle height adjust control apparatus and method for automatically adjusting a vehicle height to a predetermined target vehicle height.
2. Description of Related Art
A vehicle height adjust control apparatus described in Japanese Patent Application Laid-Open No. Hei 2-246812, for example, includes an actuator provided between a vehicle body and wheels, the actuator being capable of changing a vehicle height by fluid supplied and discharged, a supply-discharge device for supplying fluid into and discharging it from the actuator, and a vehicle height detection device for detecting a vehicle height. The supplying of fluid to and the discharging of it from the actuator performed by the fluid supply-discharge device is controlled on the basis of the detected vehicle height so that the vehicle height detected becomes equal to a target vehicle height.
In this related technology, however, if the vehicle height cannot be increased to a target vehicle height despite a considerably high fluid pressure in the fluid supply-discharge device and the actuator, due to an excessively large superimposed load, the ability of the fluid supply-discharge device and the actuator, an abnormality in the vehicle height detection by the vehicle height detection device, and the like, the fluid pressure in the fluid supply-discharge device and the actuator is further increased, or the fluid supply-discharge device and the actuator continue operating for vehicle height adjustment. Such operating conditions are unfavorable in terms of the durability or service life of the fluid supply-discharge device and the actuator. Furthermore, if the target vehicle height is reached, the pressure in the actuators and the fluid supply-discharge device becomes abnormally high, which is also unfavorable in terms of the durability or service life of the fluid supply-discharge device and the actuator. The aforementioned undesirable conditions are remarkable when the fluid temperature is low, particularly in a case where the fluid is a hydraulic oil whose viscosity greatly varies depending on temperature.